1. Field
The described aspects relate generally to systems and methods for power control in wireless communication systems. In particular, the described aspects relate to downlink outer loop power control in a wireless communication system.
2. Background
Cellular wireless communications systems generally comprise a number of radio transceivers, or base stations, that define service areas or cells. Cellular systems are designed specifically to accommodate a number of users of user equipment (UE) as the user moves around within the system. Thus, various UEs may interact with various base stations as users move through the system.
As the user moves throughout the system, power control may be used by the base station and/or the UE to ensure sufficient quality of service of signals received at the base station and/or the UE. Spread spectrum systems such as Code Division Multiple Access (CDMA) typically employ an open loop and/or closed loop power control scheme. In closed loop power control, the UE may actively participate in making power adjustments. Further, the closed loop power control typically has two loops: the inner-loop and the outer-loop. In one aspect, the inner-loop regularly measures the received signal quality at the base station and compares it to a target signal quality. This measurement may be performed on any channel or combination of channels that can be used as a power reference. For example, the UE may compare signals received from a given base station to a given threshold value, or quality of service value. Then, the base station may instruct the UE to increase or decrease transmit power based upon the comparison, to meet a signal quality target. On the other hand, the outer-loop regularly updates the signal quality target based on an estimate of the current decoding quality. For example, the outer-loop may increase the signal quality target by a first amount each time a frame is incorrectly decoded by the UE, and decrease the signal quality target by a second amount each time a frame is correctly decoded. In this manner, using the outer-loop, the UE may adjust the signal quality target for the inner-loop to a level at which a predetermined, acceptable quality of service is maintained.
Currently, in closed loop power control schemes, the current method of setting the signal quality target is based on the UE receiving data on the downlink. If the scenario occurs where all of the data being transmitted is on the uplink, however, the signal quality target may become outdated, e.g. during dormancy on the downlink channels. During such a scenario, the UE may experience lower quality of downlink and takes time to adapt to the actual channel conditions, creating performance issues and call drops for the UE during transmissions between the UE and the base station.